Complex microstructure film

ABSTRACT

The present invention is directed to an adhesive article and methods of manufacturing the adhesive article. The adhesive article comprising at least one major surface comprising a microstructured surface, the microstructured surface comprising microstructured elements, the microstructured elements comprising walls and at least one wall has variable height with a maximum height and a minimum height along the wall length.

FIELD OF THE INVENTION

[0001] The present invention relates to printable adhesive articles.

BACKGROUND OF THE INVENTION

[0002] The present invention is related to printable adhesive articles.The present invention is especially useful for linerless adhesive tapesand labels. Images and printed matter including indicia, bar codes,symbols and graphics are common. Images and data that warn, educate,entertain, advertise or otherwise inform, etc. are applied on a varietyof interior and exterior surfaces.

[0003] Techniques that may be used to print images and printed matterinclude thermal mass transfer printing (also known simply as thermaltransfer printing), dot-matrix printing, laser printing,electrophotography (including photocopying) and inkjet printing. Inkjetcan include printing by drop-on-demand inkjet or continuous inkjettechniques. Drop on demand techniques include piezo inkjet and thermalinkjet printing which differ in how the ink drops are created.

[0004] Inkjet inks can be organic-solvent based, aqueous (water-based)or solid (phase-change) inkjet inks. Solid inkjet inks have a solid waxor resin binder component. The ink is melted. The molten ink is thenprinted by ink-jet.

[0005] The components of an inkjet system used for making graphics canbe grouped into three major categories: the computer, software, andprinter category, the ink category and the category of receptor medium.

[0006] The computer, software, and printer will control the size, numberand placement of the ink drops and will transport the receptor mediumthrough the printer. The ink will contain the colorant. The receptormedium provides a repository to accept and hold the ink. The quality ofthe inkjet image is a function of the total system.

[0007] The composition and interaction between the ink and receptormedium is most important in an inkjet system. With printers nowexceeding 2400×2400 dpi resolution, inkjet drop size is smaller than inthe past. A typical drop size for this dpi precision, is less than about10 picoliters. Some printer makers are striving for even smaller dropsizes, while other printer makers are content with the larger drop sizesfor large format graphics.

[0008] Containers, packages, cartons, and cases, (generally referred toas “boxes”) for storing and shipping products typically use box sealingtape, such as an adhesive tape, to secure the flaps or covers so thatthe box will not accidentally open during normal shipment, handling, andstorage. Box sealing tape maintains the integrity of a box throughoutits entire distribution cycle. Box sealing tape can be used on otherparts of boxes and on other types of article. A typical box sealing tapecomprises a plastic film backing with a printable surface and apressure-sensitive adhesive layer. This tape can be printed and appliedto a box to seal the box. It can also be printed, cut into a label andapplied onto a box or article. These tapes can be made in roll or padform, and can have information printed or otherwise applied to, orcontained within or on, the tape.

[0009] These boxes generally display information about the contents.This information most commonly located on the box might include lotnumbers, date codes, product identification information, and bar codes.The information can be placed onto the box using a number of methods.These include preprinting the box when it is manufactured, or printingthis information onto the box at the point of use. Other approachesinclude the use of labels, typically white paper with preprintedinformation either applied manually, or with an online automatic labelapplicator.

[0010] A recent trend in conveying information related to the product isthe requirement to have the information specific for each box. Forexample, each box can carry specific information about its contents andthe final destination of the product, including lot numbers, serialnumbers, and customer order numbers. The information is typicallyprovided on tape or labels that are customized and printed on demand,generally at the point of application onto the box.

[0011] One system for printing information involves thermal transfer inkprinting onto tape or labels using an ink ribbon and a special heattransfer print head. A computer controls the print head by providinginput to the head, which heats discrete locations on the ink ribbon. Theink ribbon directly contacts the label so that when a discrete area isheated, the ink melts and is transferred to the label. Another approachusing this system is to use labels that change color when heat isapplied (direct thermal labels). In another system, variable informationis directly printed onto a box or label by an inkjet printer including aprint head. A computer can control the ink pattern sprayed onto the boxor label.

[0012] Both thermal transfer and inkjet systems produce sharp images.With both ink-jet and thermal transfer systems, the print qualitydepends on the surface on which the ink is applied. It appears that thebest system for printing variable information is one in which the inkand the print substrate can be properly matched to produce a repeatablequality image, especially bar codes, that must be read by an electronicscanner with a high degree of reliability.

[0013] Regardless of the specific printing technique, the printingapparatus includes a handling system for guiding a continuous web oftape to the print head away from the print head following printing forsubsequent placement on the article of interest (for example, a box). Tothis end, the web of tape is normally provided in a rolled form (“tapesupply roll”), such that the printing device includes a support thatrotatably maintains the tape supply roll. When the tape roll islinerless, the adhesive of the tape is in intimate contact with theprintable surface of the next wrap of tape in the roll.

[0014] Examples of microstructured ink receptor media can be found in WO99/55537, WO 00/73083, WO 00/73082, WO 01/58697 and WO 01/58698.

SUMMARY OF THE INVENTION

[0015] Using a microporous or microstructured ink receptor adhesivearticle without a liner has created special problems. Generally, theadhesive layer tends to flow into the microstructured elements of themicrostructure surface or the porous surface of the microporoussubstrate. Under certain conditions of time, pressure and temperature,the adhesive layer may become transferred or bonded to the surfacebelow. Therefore, in stacks of linerless labels or in a roll of tape,the adhesive can no longer be separated from the microstructured surfacedirectly below it. This results in either failure between the adhesiveand its backing or complete failure to remove the top layer of theadhesive article.

[0016] The present invention is directed to an adhesive article having areceptor medium comprising a microstructured surface that can be stackedinto a pad or wound into a roll of tape and maintain the removability ofthe top adhesive article or the leading edge of the tape. Specifically,the present invention is directed to an article comprising at least onemajor surface comprising a microstructured surface, the microstructuredsurface comprising microstructured elements, the microstructuredelements comprising walls and at least one wall has variable height witha maximum height and a minimum height along the wall length.

[0017] The present invention is additionally directed to a multi-layerarticle comprising a first layer and a seconf layer. The first layercomprises a first backing, the backing comprising a first major surfaceand a second major surface, wherein the first major surface comprises amicrostructured surface comprising depressed microstructured elements,wherein the microstructured elements have walls separating themicrostructured elements and at least one wall has variable height alongthe wall and a maximum height and a minimum height along the wall; and afirst adhesive layer on the second major surface of the first backing.The second layer comprises a second backing, the backing comprising afirst major surface and a second major surface, wherein the first majorsurface comprises a microstructured surface comprising depressedmicrostructured elements, wherein the microstructured elements havewalls separating the microstructured elements and at least one wall hasvariable height along the wall and a maximum height and a minimum heightalong the wall; and a second adhesive layer on the second major surfaceof the second backing. In the multilayer article, the first adhesivelayer is in contact with the first major surface of the second backing.

[0018] The present invention is further directed to a method ofmanufacturing a film comprising extruding a resin between a nip roll anda cast roll under pressure, wherein the temperature of the cast rollduring the method (T_(Process)) is lower than the temperature requiredfor full replication of the tool (T_(FR)). Generally T_(process) is atleast 5° C. lower than

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a scanning electron microscopy image of an embodiment ofthe present invention.

[0020]FIG. 2 is a transverse cross-sectional view of the embodimentillustrated in FIG. 1 along line 2-2.

[0021]FIG. 3 is a transverse cross-sectional view of the embodimentillustrated in FIG. 1 along line 3-3.

[0022]FIG. 4 is a cross-sectional view of an embodiment of the presentinvention including a multilayer structure.

[0023]FIGS. 5-6 are cross sectional views along the wall of additionalembodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0024] For the purpose of the present invention, the following termsshall be defined:

[0025] “Microstructured element” means a recognizable geometric shapethat either protrudes or is depressed.

[0026] “Microstructured surface” is a surface comprising microstructuredelements.

[0027]FIG. 1 is a scanning electron microscopy of an embodiment of thepresent invention. The optical image illustrates microstructuredelements 20 and walls 21 enclosing the microstractured elements.

[0028]FIG. 2 illustrates an adhesive article embodying features of theinvention. FIG. 2 shows a longitudinal cross sectional view of anembodiment as shown in FIG. 1 along the line 2-2. The adhesive articlecomprises a microstructured backing 212 and an adhesive layer 214. Themicrostructured backing 212 comprises a first major surface 216 and asecond major surface 218. An adhesive layer 214 is in contact with thesecond major surface 218. The adhesive layer 214 may be a continuouslayer or a discontinuous layer (e.g. stripes or dots of adhesive.)

[0029]FIG. 3 illustrates a longitudinal cross sectional view of anembodiment as shown in FIG. 1 along the line 3-3. In the embodimentillustrated in FIG. 3, the first major surface 316 of themicrostructured backing defines microstructured elements, in this casedepressed microstructured elements 320, within the first major surface316. The microstructured elements 320 have a surface 322. Themicrostructured element surface 322 may be smooth or textured (e.g.ridges defined within the microstructured element surface 322 (notshown)). The ridges may have any pattern, such as straight lines orcross-cut lines.

[0030] The microstructured elements 20 are enclosed by walls 21. Thewalls 21 illustrated in FIG. 1 have a variable height. The walls 21 havea height (i.e. height above the surface of the microstructured element22) of from about 5 to about 200 micrometers, for example between about5 and about 100 micrometers. In certain embodiments, the difference inheight between the shortest height on the wall (minimum height) and thetallest (maximum height) is between about 1 and about 50 micrometers,for example between about 1 and about 30 micrometers, and may exist atany point along the wall. In certain embodiments, the difference betweenthe minimum and the maximum height is between about 5 and about 20micrometers. For example, FIG. 3 illustrates in some embodiments thewalls 21 have intersection points 323 (i.e. where one wall meets anotherwall), and the maximum height is at the intersection point. In otherembodiments, the walls have a point 325 along the walls between any twointersection points, and the minimum height is at the point 325. Inother embodiments, the minimum height is zero (0) and a portion of thewall may be level with the microstructured element surface 322.

[0031] The walls generally have a thickness of between about 1 to about50 micrometers, for example between about 1 and about 30 micrometers. Incertain examples, the walls have a thickness of between about 5 andabout 30 micrometers.

[0032] In general, the choice of geometrical configuration of themicrostructured element has sufficient capacity to control placement ofan individual drop of ink. In some embodiments, the geometricalconfiguration is chosen such that the microstructured element pitch(that is, center to center distance between microstructured elements) isbetween about 1 and about 1000 micrometers, for example between about 10and about 500 micrometers. In specific embodiments, the pitch is betweenabout 50 and about 400 micrometers.

[0033] The microstructured elements may have any structure. For example,the structure for the microstructured element can range from the extremeof cubic elements with parallel vertical, planar walls, to the extremeof hemispherical elements, with any possible solid geometricalconfiguration of walls in between the two extremes. Specific examplesinclude cube elements, cylindrical elements, conical elements withangular, planar walls, truncated pyramid elements with angular, planarwalls, honeycomb elements and cube corner shaped elements. Other usefulmicrostructured elements are described in PCT publications WO 00/73082and WO 00/73083.

[0034] The pattern of the topography can be regular, random, or acombination of the two. “Regular” means that the pattern is planned andreproducible. “Random” means one or more features of the microstructuredelements are varied in a non-regular manner. Examples of features thatare varied include for example, microstructured element pitch, peak-tovalley distance, depth, height, wall angle, edge radius, and the like.Combination patterns may for example comprise patterns that are randomover an area having a minimum radius of ten microstructured elementwidths from any point, but these random patterns can be reproduced overlarger distances within the overall pattern. The terms “Regular”,“Random” and “Combination” are used herein to describe the patternimparted to the length of web by one repeat distance of the tool havinga microstructured pattern thereon. For example, when the tool is acylindrical roll, one repeat distance corresponds to one revolution ofthe roll. In another embodiment, the tool may be a plate and the repeatdistance would be a plate and the repeat distance would correspond toone or both dimensions of the plate.

[0035] The volume of a microstructured element can range from about 1 toabout 20,000 pL, for example from about 1 to about 10,000 pL. Certainembodiments have a volume of from about 3 to about 10,000 pL, forexample from about 30 to about 10,000 pL, such as from about 300 toabout 10,000 pL. The volumes of the microstructured elements maydecrease as printing technology leads to smaller ink drop size.

[0036] For applications in which desktop inkjet printers (typical dropsize of 3-20 pL) will be used to generate the image, microstructuredelement volumes generally range from about 300 to about 8000 pL. Forapplications in which large format desktop inkjet printers (typical dropsize of 10-200 pL will be used to generate the image, microstructuredelement volumes range from about 1,000 to about 10,000 pL.

[0037] Another way to characterize the structure of the microstructuredelements 20 is to describe the microstructured elements in terms ofaspect ratios. An “aspect ratio” is the ratio of the height of amicrostructured element to the width of a microstructured element.Useful aspect ratios for a depressed element range from about 0.01 toabout 2, for example from about 0.05 to about 1, and in specificembodiments from about 0.05 to about 0.8. Useful aspect ratios for aprotruding element range from about 0.01 to about 15, for example fromabout 0.05 to about 10, and in specific embodiments from about 0.05 toabout 8.

[0038] The overall height of the microstructured elements depends on theshape, aspect ratio, and desired volume of the microstructured element.The height of a microstructured element can range from about 5 to about200 micrometers. In some embodiments, the height ranges from about 20 toabout 100 micrometers, for example about 30 to about 90 micrometers.

[0039] Microstructured element pitch is in the range of from 1 to about1000 micrometers. Certain embodiments have a microstructured elementpitch of from about 10 to about 500 micrometers, for example from about50 to about 400 micrometers. The microstructured element pitch may beuniform, but it is not always necessary or desirable for the pitch to beuniform. It is recognized that in some embodiments of the invention, itmay not be necessary, or desirable, that uniform element pitch beobserved between microstructured elements, nor that all features beidentical. Thus, an assortment of different types of features, forexample, microstructured elements with, perhaps, an assortment ofpitches may comprise the microstructured surface. The average peak tovalley distances of individual elements is from about 1 to about 200micrometers.

[0040]FIG. 4 shows an embodiment of the present invention in amultilayer structure 400. FIG. 4 illustrates two layers of a multilayerstructure with first adhesive article 410 a and second adhesive article410 b. The first adhesive article 410 a comprises a microstructuredbacking 412 a and an adhesive layer 414 a. The microstructured backing412 a comprises a first major surface 416 a and a second major surface418 a. The second adhesive article 410 b comprises a microstructuredbacking 412 b and an adhesive layer 414 b. The microstructured backing412 b comprises a first major surface 416 b and a second major surface418 b. The first adhesive layer 414 a is in direct contact with thefirst major surface 416 b of the second microstructured backing 412 b.Therefore, in order to remove the first adhesive article 410 a from thesecond adhesive article 410 b, the first adhesive layer 414 a releasesfrom the first major surface of 416 b of the second microstructuredbacking 412 b.

[0041]FIGS. 5 and 6 illustrate different embodiments of a cross sectionof an article of the invention.

[0042] Microstructured Backing

[0043] The microstructured backing typically comprises a polymer. Thebacking can be a solid film. The backing can be transparent,translucent, or opaque, depending on desired usage. The backing can beclear or tinted, depending on desired usage. The backing can beoptically transmissive, optically reflective, or opticallyretroreflective, depending on desired usage.

[0044] Nonlimiting examples of polymeric films useful as backing in thepresent invention include thermoplastics such as polyolefins (e.g.polypropylene, polyethylene), poly(vinyl chloride), copolymers ofolefins (e.g. copolymers of propylene), copolymers of ethylene withvinyl acetate or vinyl alcohol, fluorinated thermoplastics such ascopolymers and terpolymers of hexafluoropropylene and surface modifiedversions thereof, poly(ethylene terephthalate) and copolymers thereof,polyurethanes, polyimides, acrylics, and filled versions of the aboveusing fillers such as silicates, silica, aluminates, feldspar, talc,calcium carbonate, titanium dioxide, and the like. Also useful in theapplication are coextruded films and laminated films made from thematerials listed above. More specifically, the microstructured backingis formed from polyvinyl chloride, polyethylene, polypropylene, andcopolymers thereof.

[0045] Properties of the backing used in the present invention can beaugmented with optional coatings that improve control of the inkreceptivity of the microstructured surface of the backing. Any number ofcoatings are known to those skilled in the art. It is possible to employany of these coatings in combination with the microstructured surface ofthe present invention.

[0046] One can employ a fluid management system having a variety ofsurfactants or polymers can be chosen to provide particularly suitablesurfaces for the particular fluid components of the pigmented inkjetinks. Surfactants can be cationic, anionic, nonionic, or zwitterionic.Many types of surfactant are widely available to one skilled in the art.Accordingly, any surfactant or combination of surfactants or polymer(s)that will render a polymer surface hydrophilic can be employed.

[0047] These surfactants can be coated or otherwise applied onto themicrostructured element surface of the microstructured elements in themicrostructured surface. Various types of surfactants have been used inthe coating systems. These may include but are not limited tofluorochemical, silicon and hydrocarbon-based ones wherein the saidsurfactants may be cationic, anionic or nonionic. Furthermore, thenonionic surfactant may be used either as it is or in combination withanother surfactant, such as an anionic surfactant in an organic solventor in a mixture of water and organic solvent, the said organic solventsbeing selected from the group of alcohol, amide, ketone and the like.

[0048] Various types of non-ionic surfactants can be used, including butnot limited to: fluorocarbons, block copolymers of ethylene andpropylene oxide to an ethylene glycol base, polyoxyethylene sorbitanfatty acid esters, octylphenoxy polyethoxy ethanol, tetramethyldecynediol, silicon surfactants and the like known to those skilled inthe art.

[0049] A release coating (low adhesion backsize) may additionally beapplied to the microstructured surface. The release coating may be acontinuous layer or a discontinuous layer (e.g. stripes and dots.) Therelease coating may be applied to the entire microstructured surface,including the microstructured elements, or only to certain areas of themicrostructured surface. For example, in embodiments comprisingdepressed microstructured elements, the release coating may be appliedonly to the surface and not within the microstructured elements. In someembodiments, a release material can be blended with the material used tomake the microstructured backing and incorporated into the backing.

[0050] Other coating materials may be used which are intended to improvethe appearance or durability of the printed image on the microstructuredsurface. For example, an ink-jet receptor coating may be used. Theinkjet receptor coating may comprise one or more layers. Useful inkreceptive coatings are hydrophilic and aqueous ink sorptive. Suchcoatings include, but are not limited to, polyvinyl pyrrolidone,homopolymers and copolymers and substituted derivatives thereof,polyethyleneimine and derivatives, vinyl acetate copolymers, forexample, copolymers of vinyl pyrrolidone and vinyl acetate, copolymersof vinyl acetate and acrylic acid, and the like, and hydrolyzedderivatives thereof; polyvinyl alcohol, acrylic acid homopolymers andcopolymers; co-polyesters; acrylamide homopolymers and copolymers;cellulosic polymers; styrene copolymers with allyl alcohol, acrylicacid, and/or maleic acid or esters thereof, alkylene oxide polymers andcopolymers; gelatins and modified gelatins; polysaccharides, and thelike. If the targeted printer prints aqueous dye inks, then a suitablemordant may be coated onto the microstructured surface in order todemobilize or “fix” the dyes. Mordants that may be used generallyconsist of, but are not limited to, those found in patents such as U.S.Pat. No. 4,500,631; U.S. Pat. No. 5,342,688; U.S. Pat. No. 5,354,813;U.S. Pat. No. 5,589,269; and U.S. Pat. No. 5,712,027. One specificexample of an inkjet receptor coating is a solution containing polyvinylpolymers and copolymers containing vinyl pyridine as described incopending U.S. provisional application No. 60/357,863 filed Feb. 19,2002. Various blends of these materials with other coating materials,for example a blend of a release agent and an inkjet receptor, listedherein are also within the scope of the invention.

[0051] Additionally, directly affecting the substrate by means generallyknown in the art may be employed in the context of this invention. Forexample, flame treated surfaces, corona treated surfaces (air andnitrogen), or surface dehydrochlorinated poly(vinyl chloride) could bemade into a microstructured backing as a printable substrate.

[0052] Adhesive

[0053] The microstructured backing may be formed into an adhesivearticle by the addition of an adhesive layer on the second major surfaceof the microstructured backing. The adhesive may be a pressure sensitiveadhesive. Any suitable pressure sensitive adhesive composition can beused for this invention. The pressure-sensitive adhesives can be anyconventional pressure-sensitive adhesive that adheres to both themicrostructured backing and to the surface receiving the adhesivearticle. The pressure sensitive adhesive component can be any materialthat has pressure sensitive adhesive properties including the following:(1) tack, (2) adherence to a substrate with no more than fingerpressure, and (3) sufficient ability to hold onto an adherend.Furthermore, the pressure sensitive adhesive component can be a singlepressure sensitive adhesive or the pressure sensitive adhesive can be acombination of two or more pressure sensitive adhesives.

[0054] Pressure sensitive adhesives useful in the present inventioninclude, for example, those based on natural rubbers, synthetic rubbers,styrene block copolymers, polyvinyl ethers, poly (meth)acrylates(including both acrylates and methacrylates), polyolefins, andsilicones.

[0055] The pressure sensitive adhesive may be inherently tacky. Ifdesired, tackifiers may be added to a base material to form the pressuresensitive adhesive. Useful tackifiers include, for example, rosin esterresins, aromatic hydrocarbon resins, aliphatic hydrocarbon resins, andterpene resins. Other materials can be added for special purposes,including, for example, oils, plasticizers, antioxidants, ultraviolet(“UV”) stabilizers, hydrogenated butyl rubber, pigments, and curingagents.

[0056] In a specific embodiment, the pressure sensitive adhesive isbased on styrene-isoprene-styrene block copolymer.

[0057] In one embodiment, the adhesive is a low-flow adhesive. Alow-flow adhesive is taught in U.S. Application Ser. No. 60/391,497,filed Jun. 25, 2002.

[0058] One specific embodiment of the invention has a fiber reinforcedpressure sensitive adhesive as described in co-pending U.S. applicationSer. No. 09/764,478, filed Jan. 17, 2001 and the continuation in partU.S. application Ser. No. 10/180,784, filed Jun. 25, 2002. In such anembodiment, any suitable pressure sensitive adhesive composition can beused as a matrix of adhesive for the fiber reinforced adhesive. Thepressure sensitive adhesive may be a low-flow adhesive, but somepressure sensitive adhesives that are not low-flow adhesives may stillbe adequate as a matrix for the fiber reinforced pressure sensitiveadhesive. The pressure sensitive adhesive is then reinforced with afibrous reinforcing material. Various reinforcing materials may be usedto practice the present invention. In specific embodiments, thereinforcing material is a polymer. In certain embodiments, thereinforcing material is elastomeric. Examples of the reinforcingmaterial include an olefin polymer, such as ultra low densitypolyethylene.

[0059] Additional layers of adhesive may be included on the adhesivelayer opposite the microstructured backing. For example, a secondadhesive layer may be coated on the low flow adhesive layer. The secondadhesive layer may or may not be a low flow adhesive. For example, an asecond adhesive layer that is not a low flow adhesive may be beneficialin a thin layer to maximize the tack of the adhesive article.

[0060] Method of Manufacturing the Tape

[0061] The tape comprises a microstructured film and an adhesive layer.The microstructured film has a first major surface comprising amicrostructured surface and a second major surface. The microstructuredsurface can be made in a number of ways, such as using casting, coating,or compressing techniques. For example, microstructuring the first majorsurface of the backing can be achieved by at least any of (1) casting amolten thermoplastic using a tool having a microstructured pattern, (2)coating of a fluid onto a tool having a microstructured pattern,solidifying the fluid, and removing the resulting film, or (3) passing athermoplastic film through a nip roll to compress against a tool havinga microstructured pattern. The tool can be formed using any of a numberof techniques known to those skilled in the art, selected depending inpart upon the tool material and features of the desired topography.Illustrative techniques include etching (for example, via chemicaletching, mechanical etching, or other ablative means such as laserablation or reactive ion etching, etc.), photolithography,stereolithography, micromachining, knurling (for example, cuttingknurling or acid enhanced knurling), scoring or cutting, etc.Alternative methods of forming the microstructured surface includethermoplastic extrusion, curable fluid coating methods, and embossingthermoplastic layers which can also be cured.

[0062] The compressing method uses a hot press familiar to those skilledin the art of compression molding. The pressure exerted in the presstypically ranges from about 48 kPa to about 2400 kPa. The temperature ofthe press at the mold surface typically ranges from about 50° C. toabout 200° C., for example from about 110° C. to about 170° C.

[0063] The duration time in the press typically ranges from about onesecond to about 5 minutes. The pressure, temperature and duration timeused depend primarily on the particular material being micro-embossed,and the type of microstructured element being generated as is known tothose skilled in the art.

[0064] The process conditions should be sufficient to cause the materialto flow and generally take the shape of the surface of the tool beingused. Any generally available commercial hot press may be used.

[0065] The extrusion method involves passing an extruded material orpreformed substrate through a nip created by a chilled roll and acasting roll engraved with an inverse pattern of the desiredmicrostructure. Or, an input film is fed into an extrusion coater orextruder. A polymeric layer is hot-melt coated (extruded) onto the inputfilm. The polymeric layer is then formed into a microstructured surface.

[0066] Single screw or twin screw extruders can be used. Conditions arechosen to meet the general requirements understood to one skilled in theart. For example, the temperature profile in the extruder can range from100° C. to 250° C. depending on the melt characteristics of the resin.The temperature at the die ranges from 150° C. to 250° C. depending onthe characteristics of the resin. The pressure exerted in the nip canrange from about 140 to about 1380 kPa and preferably from about 350 toabout 550 kPa. The temperature of the nip roll can range from about 5°C. to about 150° C., for example from about 10° C. to about 100° C., andthe temperature of the cast roll can range from about 25° C. to about100° C., for example about 40° C. to about 60° C. Generally thetemperature of the cast roll during the process (T_(Process)) is lowerthan the temperature required for full replication of the tool (T_(FR)).T_(FR) is the minimum temperature the cast roll should be set at toensure complete replication of the pattern in the tool to the resinfilm. T_(FR) is dependent on many factors, including the resin used, theline speed and the pressure in the nip. One of skill in the art candetermine T_(FR) for any given process conditions. T_(Process) isgenerally at least 5° C. lower than T_(FR). The speed of movementthrough the nip typically ranges from about 0.25 to about 500meters/min, but generally will move as fast as conditions allow.

[0067] Calendering may be accomplished in a continuous process using anip, as is known in the film handling arts. In the present invention, aweb having a suitable surface, and having sufficient thickness toreceive the desired microstructure pattern is passed through a nipformed by two cylindrical rolls, one of which has an inverse image tothe desired embossing engraved into its surface. The surface layercontacts the engraved roll at the nip. The web is generally heated totemperatures of from 100° C. up to 540° C. with, for example, radiantheat sources (for example, heat lamps, infrared heaters, etc.) and/or byuse of heated rolls at the nip. A combination of heat and pressure atthe nip (typically, 100 to 500 lb/inch (1.8 kg/centimeter to 9kg/centimeter)) is generally used in the practice of the presentinvention.

[0068] The second major surface of the microstructured backing isadhesive coated with an adhesive composition as described above. Thismay be accomplished using any coating technique known in the art.

[0069] The resulting adhesive article may include a release liner on theadhesive layer (not shown), though a release liner is not necessary.Release liners are known and commercially available from a number ofsources. Examples of release liners include silicone coated kraft paper,silicone coated polyethylene coated paper, silicone coated or non-coatedpolymeric materials such as polyethylene or polypropylene. Theaforementioned base materials may also be coated with polymeric releaseagents such as silicone urea, fluorinated polymers, urethanes, and longchain alkyl acrylates.

[0070] Printed Article

[0071] The adhesive article described is desirable to print. Themicrostructured elements contain any ink receptive coating and any inkapplied to the microstructured surface, resulting in a controlled image.

[0072] Method of Printing

[0073] The adhesive article may be printed by any method known in theart. Specifically, the present adhesive article may be placed into anink-jet printer and printed at high speeds (i.e. speeds in excess of 5cm/second) while maintaining a clean image.

[0074] The following examples further disclose embodiments of theinvention.

EXAMPLES

[0075] Test Methods

[0076] Microstructured Film Images and Wall Height Differential

[0077] Images of the microstructure film providing three dimensionalrelief were obtained using Scanning Electron Microscopy at amagnification of from about 40 to about 250×. The height differential ofthe walls forming the recesses was obtained by scanning white lightinterferometry. For Examples 1 (Comparative) and 2 a Wyko interferometerwas employed and for Examples 3 (Comparative) and 4-10 a Zygointerferometer was used.

[0078] Peel Adhesion Strength (Initial)

[0079] A sample of the extruded microstructured film measuring 2 incheswide by 5 inches long (5.08 by 12.7 cm) was attached to a steel plate(2×5×{fraction (1/16)} inches (5.08×12.7×0.16 cm)) using double sticktape such that the microstructured surface was exposed. This and samplesof 3M Scotch® Box Sealing Tape No. 311 (a general purpose box sealingtape having a 0.00095 inch (24 micrometer) thick pressure sensitiveacrylic adhesive on a 0.0011 inch (28 micrometer) thick biaxiallyoriented polypropylene backing, available from 3M Company, St. Paul,Minn.) were conditioned for 24 hours at 77° F. (25° C.) and 50% relativehumidity. Next, a piece of the tape measuring about 7 inches long by 1inch wide was placed lengthwise with the adhesive side down on themicrostructured surface of the film such that about 2 inches (5.08 cm)of the tape extended past the edge of the film substrate. This portionwas doubled back onto itself to provide a one inch (2.54 cm) tab. A 4.5pound (2.04 kg) rubber roller was mechanically passed over the tape oncein each direction (forward and back) at a rate of 12 inches/minute (30.5cm/minute). This assembly was then used to measure 90° angle peeladhesion strength at room temperature using an SINTECH 6 (available fromMTS Systems Corporation, Research Triangle Park, N.C.) equipped with a25 pound load cell at a jaw separation rate of 50 inches/minute (127cm/minute). The reported value was an average of 3 samples. Thisprocedure was also employed using 3M Scotch® Superior Performance BoxSealing Tape No. 375 (a superior performance packaging tape having a0.0011 inch (28 micrometer) thick pressure sensitive hot melt adhesiveon a 0.002 inch (51 micrometer) thick biaxially oriented polypropylenebacking, available from 3M Company, St. Paul, Minn.) in place of the 311tape.

[0080] Peel Adhesion Strength (Aged)

[0081] Peel adhesion strengths were measured on assemblies of steelplate/microstructured film/adhesive tape which were prepared asdescribed above in “Peel Adhesion Strength (Initial)” and aged asfollows. The assemblies were aged at 150° F. (66° C.) for 24 hours thenequilibrated for 24 hours at 77° F. (25° C.) and 50% relative humiditybefore testing for peel adhesion strength as previously described.

Example 1 (Comparative)

[0082] A microstructured film was prepared which exhibited anessentially uniform height for both the walls and intersection points ofthe walls running perpendicular to each other. More specifically, an83:17 (w:w) mixture of a clear polypropylene resin (FINA 3376, apolypropylene homopolymer resin containing calcium stearate having amelt flow rate (per ASTM D1238, 230C/2.16 kg load) of between about 2.5and about 3.1 g/10 minutes, a Hunter Color “b” of 2.0 or less, andxylene solubles of between about 3.5 and 4.5%, obtained from ATOFINAPetrochemical Company, Dallas, Tex.) and a white pigmented polypropyleneresin (a 1:1 blend by weight of titanium dioxide and PP4792 E1, apolypropylene resin having a typical melt flow rate of 2.7 g/10 minutes(230° C./2.16 kg), available from ExxonMobil Chemical, Houston, Tex.)were extruded into between two heated nip rollers located in closeproximity to the die using a Killion single screw extruder (availablefrom Davis Standard Killion, Pawcatuck, Conn.). The extruder had adiameter of 3.18 centimeters (cm) (1.25 inches), a length/diameter ratioof 30:1, and five heated zones which were set as follows: Zone 1, 124°C. (255° F.); Zone 2, 177° C. (350° F.); Zone 3, 235° C. (455° F.); Zone4, 243° C. (470° F.); and Zone 5, 249° C. (480° F.). The die temperaturewas set at 249° C. (480° F.). The molten resin exited the die and wasdrawn between two nip rollers closed under pressure. The upper nip rollwas a rubber coated roll and the lower nip roll was a metal tool rollhaving a microstructured pattern engraved on its surface. The nip rollsboth had a diameter of approximately 30.5 cm (12 inches) and were hollowto permit heating or chilling of the rolls by passing a fluid throughtheir interiors. The setpoint of the upper roll was 38° C. (100° F.) andthe setpoint of the lower roll was 110° C. (230° F.). The web speed wasbetween approximately 3.0 and 3.7 meters/minute (9.8 to 12.1feet/minute).

[0083] The metal tool roll was engraved with three sets of grooves.There were two sets of parallel grooves, which were perpendicular toeach other and are referred to hereinafter as the major grooves. Thesetwo perpendicular sets of helical grooves ran at an angle ofapproximately 45° to the roll axis, and had a depth of approximately 75micrometers (microns, or μm), a width of approximately 18 μm at thebottom and 38 μm at the top, and were spaced approximately 125 μm apart.The third set of grooves, hereinafter referred to as the minor grooves,ran at an angle of approximately 90° to the roll axis (i.e., parallel tothe web direction) and had a depth of between about 8 and about 10micrometers, a width of approximately 8 micrometers at the bottom andapproximately 11 micrometers at the top, and were spaced approximately35 μm apart.

[0084] The microstructured surface of the tool roll embossed theextruded polypropylene resin to provide a polypropylene film having afirst major surface with a microstructured pattern thereon, and a secondmajor surface. The embossed film thus obtained, having a total thicknessof about 0.0056 inches (142 micrometers), cooled prior to reaching awindup roll. The embossed pattern on the film comprised wells orrecesses separated by walls. The recesses were rhomboidal in shape witha nominal depth of 75 μm, and the walls lay at 45° to the machinedirection (web direction) of the microstructured film. In addition, thebottom of the recesses contained ridges which ran at an angle of 45° tothe direction of the walls of the recesses (that is, they ran parallelto the web direction) and which had a nominal height of between 8 and 10μm, a width at the top of about 8 micrometers and at the bottom of about11 micrometers, and which were spaced approximately 35 μm apart.Inspection with a Wyco Interferrometer microscope (Model RST, obtainedfrom Veeco Metrology Group, Tucson, Ariz.) revealed essentially uniformwall heights along their lengths including the intersection points wherethe walls that ran perpendicular to each other crossed. The ridgeheights also appeared to be uniform.

Example 2

[0085] Example 1 was repeated with the following modification. The metaltool roll had a temperature setpoint of 99° C. (210° F.). Themicrostructured film thus obtained, having a total thickness of 0.0050inches (127 micrometers), inspected by interferrometer. It was observedthat the walls possessed a saddle-like shape with respect to theirheight. There was a minimum in the wall height at a position between theintersection points and a maximum in the region of the intersectionpoints, with the height differential being approximately 14 μm. Theridges in the bottom of the recesses exhibited a uniform height.

Examples 3 (Comparative) and 4-7

[0086] Microstructured films were prepared which exhibited varyingdegrees of height differential between the intersection points of thewalls running perpendicular to each other and a point along the walllength between the intersection points. These were evaluated for theirrelease characteristics from adhesive tapes both initially and afteraging at elevated temperature and for their wall height differential.More specifically, clear polypropylene resin (Homopolymer 4018 InjectionMolding Resin having a melt flow rate of 13.5 g/10 minutes (230° C./2.16kg), available from BP Amoco Polymers, Naperville, Ill.) was extrudedinto between two heated nip rollers located in close proximity to theexit die using a Davis Standard single screw extruder (available fromDavis Standard Killion, Pawcatuck, Conn.). The extruder had a diameterof 6.35 cm (2.50 inches), a length/diameter ratio of 38/1, and sixheated zones which were set as shown in Table 1 below. Also shown inTable 1 are the actual feedblock and die temperatures.

[0087] The molten resin exited the die and was drawn between two niprollers closed under pressure. The upper nip roll was a rubber coatedroll and the lower nip roll was a metal tool roll having amicrostructured pattern engraved on its surface. This pattern wascomprised of major grooves and minor grooves like that described inExample 1 with the following modification. The set of minor grooves hada depth of between about 4 and about 5 micrometers, a width ofapproximately 8 μm at the bottom and approximately 11 μm at the top, andwere spaced approximately 35 μm apart. The nip rolls both had a diameterof approximately 45.7 cm (18 inches) and were hollow to permit heatingor chilling of the rolls by passing a fluid through their interiors. Thetemperatures of the upper rubber roll and lower metal, as well as theweb speeds, for each example are given in Table 1 below.

[0088] The total film thicknesses for Examples 1-10 are shown in Table 3below. The resulting microstructured films were evaluated for their wallheight differential and their release characteristics from an adhesivetape both initially and after aging at elevated temperature as describedin the test methods above. The results are shown in Table 4 below. TABLE1 Example Parameters 3 (Comparative) 4 5 6 7 Feedblock 238 238 238 238238 ° C. (° F.) (460) (460) (460) (460) (460) Zone 1 108 108 120 147 147° C. (° F.) (226) (226) (248) (297) (297) Zone 2 182 182 182 183 182 °C. (° F.) (360) (360) (360) (361) (360) Zone 3 204 204 204 204 204 ° C.(° F.) (400) (400) (400) (400) (400) Zone 4 216 216 216 216 215 ° C. (°F.) (420) (420) (420) (420) (419) Zone 5 216 216 216 216 216 ° C. (° F.)(420) (420) (421) (420) (420) Zone 6 216 216 216 216 214 ° C. (° F.)(420) (420) (420) (420) (418) Die 238 238 238 238 238 ° C. (+ F.) (460)(460) (460) (460) (460) Rubber Roll  21  22  16  16  16 ° C. (° F.) (70)  (71)  (61)  (61)  (61) Tool Roll  77  77  71  63  57 ° C. (° F.)(170) (170) (160) (145) (135) Web Speed  5.36  9.14  13.7  18.3  22.9meters/minute  (17.6)  (30.0)  (45.0)  (60.0)  (75.0) (feet/minute)

Examples 8-10

[0089] Microstructured films were prepared which exhibited varyingdegrees of height differential between the intersection points of thewalls running perpendicular to each other and a point along the walllength between the intersection points. These were evaluated for theirrelease characteristics from adhesive tapes both initially and afteraging at elevated temperature and for their wall height differential.More specifically, an 83:17 (w:w) mixture of a clear polypropylene resin(Homopolymer 4018 Injection Molding Resin, available from BP AmocoPolymers, Naperville, Ill.) and a white pigmented polypropylene resinlike that used in Example 1 was extruded into a microstructured filmusing the procedure described for Examples 3 (Comparative) and 4-7above. The zone, feedblock, die, rubber roll, and metal rolltemperatures, as well as web speeds, are shown in Table 2 below.

[0090] The resulting microstructured films thus obtained, having a totalthickness of about 0.0055 inches (140 micrometers), were evaluated theirwall height differential and their release characteristics from anadhesive tape both initially and after aging at elevated temperature asdescribed in the test methods above. The results are shown in Table 4below. TABLE 2 Example Parameters 8 9 10 Feedblock 238 227 227 ° C. (°F.) (460) (440) (440) Zone 1 153 158 158 ° C. (° F.) (308) (316) (316)Zone 2 182 193 193 ° C. (° F.) (360) (380) (380) Zone 3 205 204 204 ° C.(° F.) (401) (400) (400) Zone 4 216 216 216 ° C. (° F.) (421) (420)(420) Zone 5 216 227 227 ° C. (° F.) (421) (440) (440) Zone 6 216 227227 ° C. (° F.) (420) (440) (440) Die 238 227 227 ° C. (° F.) (460)(440) (440) Rubber Roll  54  54  54 ° C. (° F.) (130) (130) (130) ToolRoll  57  57  57 ° C. (° F.) (135) (135) 135 Web Speed   22.9   22.9  22.9 meters/minute (feet/minute)   (75.0)   (75.0)   (75.0)

[0091] TABLE 3 Example 1 2 3 4 5 6 7 8 9 10 Thickness 5.6 5.0 8.5 5.95.9 6.3 5.6 5.5 5.5 5.5 (inches/1000) Thickness 142 127 216 150 150 160142 140 140 140 (μm)

[0092] TABLE 4 Tape 311 Tape 311 Tape 375 Tape 375 Height Initial AgedInitial Aged Differential (oz./inch) (oz./inch) (oz./inch) (oz./inch)Example (micrometers) (N/cm) (N/cm) (N/cm) (N/cm) 3 0 9.0 16.7 23.7 17.0(Comparative) (0.975) (1.81) (2.57) (1.84) 4 1 9.7 17.0 27.3 17.7 (1.05)(1.84) (2.96) (1.92) 5 3 9.0 15.3 25.7 17.3 (0.975) (1.66) (2.78) (1.87)6 3 8.7 14.3 28.7 16.0 (0.942) (1.55) (3.11) (1.73) 7 10 7.3 16.0 27.315.0 (0.791) (1.73) (2.96) (1.62) 8 14 5.3 11.7 24.0 13.3 (0.574) (1.27)(2.60) (1.44) 9 13 5.0 11.0 22.3 12.7 (0.541) (1.19) (2.42) (1.38) 10 136.3 13.0 22.7 13.3 (0.682) (1.41) (2.46) (1.44)

[0093] Various modifications and alterations of the present inventionwill become apparent to those skilled in the art without departing fromthe spirit and scope of the invention.

1. An article comprising at least one major surface comprising a microstructured surface, the microstructured surface comprising microstructured elements, the microstructured elements comprising walls and at least one wall has variable height with a maximum height and a minimum height along the wall length.
 2. The article of claim 1 wherein at least two walls intersect, and the wall height at the intersection point is the maximum height along the wall.
 3. The article of claim 2 wherein between any two intersection points along a wall is a point having the minimum height along the wall.
 4. The article of claim 2 wherein the point midway between any two intersection points along a wall is a center point, and the center point is the minimum height along the wall.
 5. The article of claim 1 wherein the maximum height is between about 5 and about 200 micrometers.
 6. The article of claim 1 wherein the minimum height is between about 0 and about 200 micrometers.
 7. The article of claim 1 wherein the difference between the maximum height and the minimum height is between about 1 and about 50 micrometers.
 8. The article of claim 1 wherein the difference between the maximum height and the minimum height is between about 1 and about 30 micrometers.
 9. The article of claim 1 wherein the difference between the maximum height and the minimum height is between about 5 and about 20 micrometers.
 10. A multi-layer article comprising a first layer comprising a first backing, the backing comprising a first major surface and a second major surface, wherein the first major surface comprises a microstructured surface comprising depressed microstructured elements, wherein the microstructured elements have walls separating the microstructured elements and at least one wall has variable height along the wall and a maximum height and a minimum height along the wall; and a first adhesive layer on the second major surface of the first backing; and a second layer comprising a second backing, the backing comprising a first major surface and a second major surface, wherein the first major surface comprises a microstructured surface comprising depressed microstructured elements, wherein the microstructured elements have walls separating the microstructured elements and at least one wall has variable height along the wall and a maximum height and a minimum height along the wall; and a second adhesive layer on the second major surface of the second backing, wherein the first adhesive layer is in contact with the first major surface of the second backing.
 11. A method of manufacturing a film comprising extruding a resin between a nip roll and a cast roll under pressure, wherein the temperature of the cast roll during the method (T_(Process)) is lower than the temperature required for full replication of the tool (T_(FR)).
 12. The method of claim 10 wherein T_(Process) is at least 5° C. lower than T_(FR). 